EP2273181A2 - Holder element for LED module - Google Patents

Abstract

The element (1) has a metallic core (2) including an oxide ceramic layer (22) on a sub-region of an upper surface (21). The oxide ceramic layer is porous, and a conductor path is aligned on a side of the oxide ceramic layer and turns away from the metallic core. An LED stays in contact with the conductor path, and the oxide ceramic layer has a thickness of about 5 to 400 micrometers, where the element forms an outer surface in the sub-region. The oxide ceramic layer defines a non-layer upper surface topology on a side facing toward the metallic core. An independent claim is also included for a method for manufacturing a carrier element for an LED.

Description

The present invention relates to a thermally conductive carrier element with a ceramic insulation layer for use with LEDs (light-emitting diodes).

The progressive development in the field of LED technology allows ever brighter LEDs. The use of high-power LED components makes it possible to produce both indoor and outdoor luminaires based on LEDs as the light source. The individual LEDs are usually arranged on a carrier element. The high performance of the LEDs often results in high power dissipation. This can cause overheating of the LEDs, which can lead to a degradation of the device properties, premature aging or early failure of the LEDs. To avoid this, effective cooling of the LEDs is required. In this case, it is of technical advantage if the cooling takes place via the carrier element itself in order to reduce additional expenditure and associated costs. However, this additional requirement for the carrier element is associated with further requirements, such as e.g. to reconcile the electrical insulation.

From the prior art heat sinks are known, which consist entirely of ceramic, and on which electrical components can be applied directly. Such heatsinks realize the required electrical isolation of the electrical circuit to its environment. Due to the high thermal resistance of the ceramic materials used, however, there is a less pronounced cooling of the components compared to metallic heat sinks.

This disadvantage avoids the in DE 10 2007 064 075 A1 disclosed prior art. There, a circuit carrier made of aluminum is disclosed, whose surface is oxidized by anodic oxidation in the so-called anodizing process. By means of the oxide layer is an electrical insulation between the metallic region of the circuit substrate and the on produced printed circuit. Due to the low thermal resistance of aluminum, a significant cooling effect can be achieved. The use of such an oxide layer for electrical insulation produced by anodic oxidation, however, has the disadvantage that the resulting layer has a high porosity. During operation, electrical flashovers from the circuits to the metallic region of the circuit carrier can arise through the pores. By contrast, if the pores are closed, for example by impregnation, the adhesive strength of the applied circuits on the oxide layer is generally reduced. In addition, the layers produced by this method are usually less than about 25 microns thick.

The object of the present invention is to provide a support element for LEDs, which has optimized properties with respect to the thermal conductivity, as well as a good electrical insulation capability and in particular has a high resistance to electrical flashovers.

The invention achieves the object by providing a carrier element, which comprises a metallic core, which is provided with an oxide ceramic layer at least in a partial region of its surface. In this case, the oxide ceramic layer has a porosity which increases from the boundary surface between the metallic core and the oxide ceramic layer in the direction of the surface of the oxide ceramic layer. Due to the low porosity near the interface with the metallic core, a high resistance to electrical flashovers is achieved. In addition, the increased porosity on the surface of the oxide ceramic layer provides good adhesion for applied printed conductors and LEDs or other electrical or electronic components (e.g., LED control chips). LEDs are also OLEDs to understand. These are particularly suitable for surface application.

For the production of the insulating oxide ceramic layer, according to one embodiment of the invention, a plasma-chemical method with spark discharge can be used. In this process, an oxide ceramic layer is formed on the metal surface in an electrolyte under plasma conditions. The metallic core is arranged as an electrode in the electrolyte. By applying a sufficiently high voltage, spark discharge occurs at the surface of the metal. This produces an oxygen plasma, through which the oxide ceramic layer forms. The metal ions in the oxide ceramic layer originate from the metallic core, the oxygen from the electrolyte used. During this process, the oxide ceramic melts. However, the melt is rapidly cooled on the side toward the electrolyte through it, leaving the migrating gases, in particular oxygen and water vapor in the oxide ceramic layer a weitmaschig linked capillary system. As a result, the oxide ceramic layer has a porosity which increases toward the surface from the metallic core.

According to one embodiment of the invention, the pore size at the interface with the metallic core is 0.7 μm and less, and the pore size at the surface of the oxide ceramic layer is 1.3 μm or more. There are also significantly smaller pores of less than 0.1 microns in diameter at the interface to the metallic core and larger pores of more than 30 microns in diameter at the surface possible.

According to one embodiment, the metallic core of the carrier element comprises a metal with a thermal conductivity of more than 40 W / (mK). In a preferred embodiment, the material is aluminum. Due to the good thermal conductivity of aluminum, which is typically about 210 W / (mK), a particularly good thermal conductivity of the carrier element is achieved. Furthermore, aluminum is a relatively inexpensive material, which is also characterized by a low density and thereby achieved low weight of the overall arrangement. In addition, the application of the described method to aluminum produces an aluminum oxide layer, which may also comprise corundum, and which has particularly advantageous technical properties. Thus, the thermal conductivity of the alumina produced is typically above about 10 W / (mK), in particular about 30 W / (mK). This high thermal conductivity of the oxide ceramic layer causes a particularly efficient dissipation of the heat loss in the LEDs. In addition, aluminum oxide has a particularly good electrical insulation capability. According to embodiments of the invention, the specific electrical conductivity of the acting as an insulator oxide ceramic layer is less than 10 ^-14 Ω ^-1 m ^-1 at room temperature. In further embodiments, the carrier element comprises another metal on which an oxide ceramic layer can be produced by means of a plasma-chemical process, such as titanium, tantalum, zirconium, niobium, haffnium, antimony, tungsten, Molybdenum, vanadium, bismuth or magnesium. According to the invention, it is also possible to use an alloy comprising one of the metals mentioned.

According to a preferred embodiment, electrical conductor tracks and / or electrical components are applied directly to the oxide layer. In this case, it is advantageous that the near-surface pore-rich oxide ceramic layer produced according to the invention has good adhesion. In this way, an additional assembly step, as it would be necessary when using an additional board, can be avoided. Furthermore, the absence of a further intermediate layer for arranging the printed conductors results in increased reliability and better thermal coupling of the components.

According to one embodiment, the thickness of the oxide ceramic layer is between about 5 μm and about 400 μm, in particular between about 25 μm and 200 μm, particularly preferably between about 40 μm and about 160 μm. The layers produced by means of conventional anodic oxidation in the so-called anodized process typically have a thickness of less than about 25 μm. By the use according to the invention of a plasma-chemical process with spark discharge, on the other hand, significantly thicker layers can be produced. Such high layer thicknesses provide increased resistance to electrical breakdown and increased resistance to corrosion, mechanical abrasion and scratches. Alternatively, the oxide ceramic layer according to the present invention can also be applied by thermal spraying. In a further embodiment, the oxide ceramic layer can also be applied by printing.

According to a preferred embodiment, moreover, the metallic core of the carrier element serves as a heat sink. For this purpose, the metallic core can have surface-enlarging structures in partial areas of its surface which are not provided with conductor tracks and LEDs. Preference is given to rib-like or lenticular surface profiles. In particular, in cooperation with the use of aluminum as a material for the metallic core, there is an advantage to simultaneously use the metallic core of the carrier element as a heat sink. The high thermal conductivity of aluminum helps to dissipate the heat loss generated in the LEDs efficiently from the LEDs. Due to the design of the carrier element as a heat sink, in some embodiments In addition, to dispense with the use of another, separate heat sink.

The metallic core is occupied on subregions of its surface with the oxide ceramic layer. In one embodiment, the entire surface of the core is coated with the oxide ceramic layer.

The LED carrier element can be used for exterior and interior lighting. In particular, in some embodiments, the surface of the carrier element occupied by LEDs can form a surface of a lamp in partial areas. Further, the support member may be provided in portions of its surface with means for fixing the lamp to a light carrier, such as. a mast or a rail. For this purpose, the carrier element may be e.g. be provided with an eyelet, a recess, a projection or a thread. In one embodiment, the carrier element may be formed so that an at least partially transparent cover can be attached to it, which serves as a light exit means. The carrier element and the transparent cover are components of a lamp housing. In particular, such an arrangement offers the advantage that the LEDs are protected from environmental influences such as e.g. Dust or moisture are protected. This is advantageous in addition to the use as a room lamp, especially for outdoor lights. Similar devices such as for attachment to a light carrier can be provided on the support member also for fixing the at least partially transparent cover and / or for attachment of optics or reflectors for directing the light of the LEDs.

The invention may further provide that the carrier element is arranged on a heat sink, with which it is in thermal contact, or forms the heat sink itself. The heat sink may in particular comprise a metallic material such as aluminum or copper. The thermal contact between the carrier element and the heat sink can be further improved by the use of a thermally conductive material, in particular a thermal grease. Overall, results from the use of a heat sink improved heat dissipation. By using another thermally conductive material, such as a thermal grease, an additional Thermal resistance for the transition of heat from the support element to the heat sink kept low.

According to a further embodiment, the oxide ceramic layer has a non-planar surface in partial areas. In particular, by using a curved metallic core, a large selection of curved surfaces can be produced by spark plasma discharge using a plasma-chemical process. In this case, the emission characteristic of a luminaire can be adjusted by means of a curved surface of the carrier element. By using a curved surface, LEDs can be spatially aligned in a desired manner. The light distribution of the luminaire can thereby be optimized for specific applications. For example, in an embodiment in which the support element for an LED module is used in the field of street lighting, the use of a curved-surface support element can set a light distribution which achieves uniform illumination of the roadway and thereby disturbing glare effects as well as excessive illumination Avoid lighting off the road.

In a further embodiment, electronic components other than LEDs are arranged on the surface of the carrier element. For example, in addition to the LEDs, electronic components may also be arranged for their activation on the carrier element. Furthermore, sensors, in particular temperature sensors, can also be arranged on the carrier element.

Figur 1

zeigt eine Teilansicht eines erfindungsgemäßen Trägerelements im Quer- schnitt, die eine keramische Isolationsschicht aufweist,

Figur 2

zeigt eine Teilansicht eines erfindungsgemäßen Trägerelements mit aufge- brachten Leiterbahnen und LED im Querschnitt.

Figur 3

zeigt eine vergrößerte Teilansicht einer erfindungsgemäßen Oxidkeramik- schicht im Querschnitt.

Further features and advantages of the invention will become apparent from the following description of a preferred embodiment of the invention with reference to the accompanying drawings.

FIG. 1

shows a partial view of a carrier element according to the invention in cross-section, which has a ceramic insulating layer,

FIG. 2

shows a partial view of a carrier element according to the invention with applied conductor tracks and LED in cross section.

FIG. 3

shows an enlarged partial view of an oxide ceramic layer according to the invention in cross section.

The figures show the structure of the carrier element according to the invention. The carrier element 1 has a metallic core 2. A portion 21 of the surface of the metallic core 2 is provided with an oxide ceramic layer 22.

The oxide ceramic layer 22 is produced on the metallic core 2 by being oxidized in the partial region 21 of its surface by means of a plasma-chemical process under spark discharges. This is done in particular by anodic oxidation in an aqueous electrolyte, under plasma conditions, a gas-solid reaction takes place, in which liquid metal is generated by a high energy input to the metallic core, which is connected as an anode. This forms a short-time fused oxide with activated oxygen.

On a metal such as aluminum in particular is a barrier layer. By increasing the voltage during this process, the barrier layer grows on the metallic core, which is poled as an anode. Then arises at the phase boundary metal / gas / electrolyte, an oxygen plasma, through which the oxide ceramic layer 22 is formed. Here, the metal ion in the oxide ceramic layer comes from the metallic core 2, while the oxygen comes from anodic reaction in the electrolyte used. The oxide ceramic is liquid at the entering plasma conditions. On the side toward the metallic core 2, the time is sufficient for the oxide ceramic melt to contract well, thus forming a sintered, low-pore oxide ceramic layer 22. Toward the side of the electrolyte, the melt of the oxide ceramic is rapidly cooled by the electrolyte, and the outflowing gases, especially oxygen and water vapor, leave an oxide ceramic layer with a wide-meshed capillary system. By this method, the oxide ceramic layer 22 has a porosity which increases from the side facing the metallic core 2 toward the surface of the layer. This is schematically in FIG. 3 shown. The portion of the oxide ceramic layer 22 adjacent to the metallic core 2 has a high resistance to electrical discharges due to its low porosity. The metallic core 2 on the other hand, its high porosity makes it suitable to provide good adhesion for printed conductors.

On the surface of the oxide ceramic layer 22 facing away from the metallic core 2, as in FIG FIG. 2 shown, printed conductors 3 and LEDs 5 are arranged. In one embodiment, the LEDs 5 are contacted by means of sockets 4 with the conductor tracks 3. In particular, a plurality of LEDs 5 can be mounted with the aid of the same base 4. Furthermore, the LEDs 5 can alternatively be contacted directly with the conductor tracks 3 without the use of a socket. This is particularly advantageous in the case of a high population density of the LEDs. The conductor tracks 3 may comprise, for example, aluminum, copper, silver or their alloys. In particular, in connection with the use of carrier elements with a curved surface, the problem thereby arises of attaching the conductor tracks 3 to the surface of the oxide ceramic layer 22. In this case, in particular a printing process such as pad printing is advantageous, as it is used for printing on plastic bodies. By using this method, there is a significant advantage over known lighting assemblies in which planar LED modules are often placed at an angle to each other to produce a desired light distribution curve. The separately arranged LED modules are usually connected to each other by an external wiring. This requires a considerable installation effort and also causes reliability risks. In contrast, the use of a curved-surface support member enables a structure in which the LEDs are disposed on a single support member. Furthermore, an elaborate wiring of the individual LEDs can be avoided by the application in particular of the pad printing method by contacting takes place via conductor tracks, which are arranged directly on the surface of the oxide ceramic layer. The avoidance of cabling outside of the support element thus reduces the assembly effort and at the same time increases the reliability of the structure. The latter effect is particularly advantageous for outdoor lamp LED carrier elements, in particular in an application for traffic route lighting, signal light, facade lighting and lighting in electrical equipment (eg in screen displays) and vehicles in harsh environmental conditions or for all types of indoor and outdoor lights.

Alternatively, screen printing or stencil printing methods are possible for applying the conductor tracks. Furthermore, galvanic methods based on chemical or electrolytic or PVD (physical vapor deposition) method can be used. Furthermore, the use of a subtractive method, such as an etching or laser process possible. Likewise, the tracks may be applied by a combination of these methods. For example, a screen printing process can be used to apply a primer to which a thin copper layer is applied by chemical plating, which can then be reinforced by electrolytic plating.

In addition to the conductor tracks 3, LEDs 5 are arranged on the surface of the oxide ceramic layer. For fixing the LEDs, a soldering, bonding or bonding method can be used. The use of a thermally highly conductive material for the carrier element results, in particular when using a soldering or bonding method, the problem that the heat required for the fastening method is quickly removed by the carrier element. Therefore, it is usually necessary to introduce a higher amount of heat during the process in order to achieve the required temperatures. However, this can lead to a thermal overload of the LEDs. In order to avoid this disadvantage, in particular the use of a vapor-phase soldering process is advantageous. In this method, the LED-equipped and solder-coated carrier element can be brought into a treatment chamber with hot steam. The steam heats the carrier element, melts the solder paste and creates the solder connection between the LEDs and the carrier element. Due to the short exposure time and the good heat transfer of condensing on the surface of the soldering steam only the surface of the solder is heated, without a larger amount of heat gets into the solder. The thermal load on the temperature-sensitive LEDs, which can lead to the destruction of the LEDs, is thereby reduced.

The metallic core 2 has the function to provide a stable support for the LED array, as well as a medium for effective heat dissipation from the LEDs. The oxide ceramic layer 22 has the function of providing an electrical insulation between the conductor tracks 3 and the metallic core 2 of the carrier element. The increased porosity near the surface of the oxide ceramic layer causes good adhesion of the Tracks 3 and the LEDs, which results in improved reliability of the structure, including thermal and mechanical stress.

The heat loss generated in the LEDs 5 is essentially forwarded by the oxide ceramic layer 22 to the metallic core 2. This is due to its good thermal conductivity property able to dissipate the heat loss quickly from the part of its surface, which is equipped with the tracks 3 and electrical components.

Numerous modifications of the illustrated preferred embodiments of the invention are possible without departing from the scope of the invention as set forth in the claims. In particular, the curvature of the surface occupied by LEDs of the carrier element or the surfaces of the oxide ceramic layer may be designed differently or the surface may also be flat.

Further, the metallic core 2 may be directly formed as a heat sink by, for example, on one side, preferably the side opposite to the surface occupied by LEDs, provided with cooling fins or similar surface enlarging structures.

LIST OF REFERENCE NUMBERS

1

support element

2

Metallic core

3

conductor tracks

4

base

5

LEDs

21

subregion

22

oxide ceramic

Claims (15)

An LED support element comprising: a metallic core (2) having an oxide ceramic layer (22) on at least a portion of its surface (21), the oxide ceramic layer (22) having a porosity increasing from the interface with the metallic core (2) toward the surface of the support member . at least one conductor track (3), which is arranged on a partial region on the side of the oxide ceramic layer (22) facing away from the metallic core (2), and at least one LED (5), which is in electrical contact with the conductor track (3). The LED support element (1) according to claim 1, wherein the oxide ceramic layer (22) is between about 5 μm and about 400 μm, in particular between about 25 μm and about 200 μm, particularly preferably between about 40 μm and about 160 μm thick. The LED support element (1) according to any one of the preceding claims, wherein the metallic core (2) comprises a material selected from aluminum, titanium, tantalum, niobium, zirconium, magnesium, haffnium, antimony, tungsten, molybdenum, vanadium, bismuth and alloys comprising one or more of these metals. LED support element (1) according to one of the preceding claims, wherein the oxide ceramic layer (22) comprises alumina, in particular corundum. LED support element (1) according to one of the preceding claims for a luminaire, wherein the support element comprises means for fixing the luminaire to a luminous support, e.g. a mast or a rail. LED support element (1) according to one of the preceding claims, wherein the oxide ceramic layer (22) defines a non-planar surface topology on the side facing away from the metallic core (2). Luminaire comprising an LED support element (1) according to one of the preceding claims. Luminaire according to claim 7, wherein the LED support element (1) forms an outer surface of the luminaire, at least in some areas. Luminaire according to claim 7 or 8, wherein the LED support element (1) forms, at least in some areas, a surface of the luminaire behind a transparent cover. Method for producing a carrier element (1) for one or more LEDs, wherein the carrier element (1) comprises a metallic core (2) and at least one partial region (21) of the surface of the metallic core (2) is provided with at least one oxide ceramic layer (22) wherein conductor tracks are arranged on the oxide ceramic layer, characterized by producing the oxide ceramic layer (22) by means of a plasma-chemical method with spark discharge or by means of thermal spraying. The method of claim 10, further comprising: applying the conductor tracks (3) to the oxide ceramic layer (22) by means of a tampon printing method or a screen printing method. The method of claim 10, further comprising: an application of the conductor tracks (3) on the oxide ceramic layer (22) by thermal spraying or cold gas spraying. A method according to any one of claims 10 to 12, wherein the metallic core (2) comprises a metal selected from aluminum, titanium, tantalum, niobium, zirconium, magnesium, haffnium, antimony, tungsten, molybdenum, vanadium, bismuth and alloys. which comprise one or more of these metals. Method according to one of claims 10 to 13, wherein the oxide ceramic layer (22) between about 5 microns and about 400 microns, in particular between about 25 microns and about 200 microns, more preferably between about 40 microns and about 160 microns thick. Method according to one of claims 10 to 14, wherein the carrier element (1) during the coating is at least partially in an electrolyte solution.

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